1. Field of the Invention
This invention relates to a camera having means for making a discrimination between an exposed state and an unexposed state of a film in use.
2. Description of the Related Art
The products of the prior art related to this invention include a camera disclosed in U.S. Pat. No. 4,878,075. This camera is arranged to find whether a film has already been exposed or not according to presence or absence of a signal reproduced from a magnetic recording part provided on the film. Another camera which has been disclosed in U.S. Pat. No. 5,049,913 is arranged to judge whether a film has been exposed from the rotated position of a rotary disk which is provided with a black-and-white pattern and is disposed on a film cartridge. A further example of a camera of this kind disclosed in Japanese Laid-Open Patent Application No. HEI 4-343353 is provided with a movable light-blocking window for the same purpose. However the cameras cited by way of example here have presented the following shortcomings.
1) The disclosure made in U.S. Pat. No. 4,878,075, for example, includes no description relative to an amount of information to be used in deciding whether or not each frame on the film has been exposed. It thus shows no countermeasures against inadequate reproduction resulting from a decrease in the amount of information due to dust sticking to a magnetic head and a malfunction resulting from an increase in the amount of information due to an external noise.
2) U.S. Pat. Nos. 4,878,075 and 5,049,913 disclose no particular arrangement in respect to selection between one means for deciding an exposed state of the film from information provided on a film cartridge and another means for deciding it for each frame of the film from magnetic information provided on the film. The lack of disclosure in this respect tends to cause a part of the film to be discarded in an unexposed state in case where the film has been exposed or used only in part in actuality while indication on the film cartridge shows that the whole film has been exposed.
3) U.S. Pat. No. 5,049,913 and Japanese Laid-Open Patent Application No. HEI 4-343353 disclose nothing about making a discrimination between an exposed state and an unexposed state as in relation to an opening or closing action on a movable light-blocking window provided on the film cartridge. The lack of disclosure in that respect tends to cause the movable light-blocking window to be wastefully opened while the film in the cartridge has been decided or judged to have been exposed.